Prior-art pressurized dispensers include both single-chamber and dual-chamber types. In the dual-chamber dispensers known in the art, serious problems involving the manner of collapse of the inner containers have been encountered. Specifically, many of these known inner containers are prone to forming pockets in which the product to be dispensed is trapped. This trapped product cannot be expelled from the inner container and is therefore wasted.
A number of approaches have been employed in attempting to solve the problem of product entrapment in the inner container of dual-chamber pressurized dispensers. For example, spreader rings or frames have been disposed within the inner container to control the manner of its collapse and thereby make it predictably free of pockets of entrapped product. However, this approach adds additional structural elements to the dispenser, thereby increasing the complexity and cost of manufacture. In addition, the spreader rings and frames can cause rupture of the inner container in the regions of contact therewith as the inner container collapses and discharges the product container therein. Also, relatively high propellant pressures are necessary to collapse such inner containers.
Another approach to the problem of product entrapment is to form the inner container with either vertical or horizontal pleats. The inner containers having vertical pleats are of an extremely complex geometry and are difficult to form by existing techiques. In addition, the sharp edges of the pleats cause high localized stresses, particularly when the inner container is formed of metal. These stresses frequently cause cracking and rupture of the inner container, resulting in spillage of the product from its chamber into the propellant chamber and consequent disabling of the dispensing device. The inner containers having horizontal pleats suffer from all of these disadvantages, and in addition cannot be reduced in diameter for insertion through the small opening at the top of the outer container.